Starship Asterisk*

Bilyous wrote:Why, in the text, is this past supernova event called a "catastrophe"? Isn't that a bit judgmental and anthropocentric? Isn't this a natural phenomenon that does not, as far as we know, involve loss of life or property?

Eric wrote:If the estimated age of the supernova event is 40,00 years, and it's 3,000 light years away, doesn't that mean the first light reached us about 37,000 years ago - not about 40,000 years ago as stated?

APOD Robot wrote:This supernova remnant has an estimated age of about 40,000 years - meaning light from the massive stellar explosion first reached Earth 40,000 years ago.

biddie67 wrote:Like Eric above, I have a problem with the "40,000 years age" of the SN remnant - but in a different way. If the light first reached Earth 40,000 years ago (estimated) -AND- the SN remnant is 3000 LY out from Earth, then it seems that the event took place 43,000 years ago ....

I wonder how the estimate of the SN remnant's light reaching Earth 40,000 years ago can be made - light doesn't leave behind fossil remains or something that can be carbon-dated ?????

nstahl wrote:

Bilyous wrote:
Why, in the text, is this past supernova event called a "catastrophe"? Isn't that a bit judgmental and anthropocentric? Isn't this a natural phenomenon that does not, as far as we know, involve loss of life or property?

One definition via Google of "catastrophe" is "a sudden violent change in the earth's surface" so this surely qualifies.

nstahl wrote:

Eric wrote:
If the estimated age of the supernova event is 40,00 years, and it's 3,000 light years away, doesn't that mean the first light reached us about 37,000 years ago - not about 40,000 years ago as stated?

That depends on what you mean by "age". If it means it took the shock wave 40,000 years from the supernova to get where they were when the photons now hitting our lenses left there, no, the time interval here is the same as the one there so the supernova photons reached earth 40,000 years ago. On the other hand if "age" means it was a total of 40,000 years including shock wave expanding and the light getting here, then yes. Since they explicitly stated the photons got here 40,000 ya I presume they intend us to understand it took the shock wave 40,000 years to expand that much.

http://upload.wikimedia.org/wikipedia/commons/thumb/a/a2/Opabinia_BW2.jpg/220px-Opabinia_BW2.jpg wrote:

[url=http://www.flickr.com/photos/34889849@N03/4405782041/]Seimeis 147 in 3D[/url]

---

Cambrian Opabinia's closest living relative: The tardigrades

<<Tardigrades (commonly known as water bears or moss piglets) form the phylum Tardigrada, part of the superphylum Ecdysozoa. They are microscopic, water-dwelling, segmented animals with eight legs. Tardigrades were first described by Johann August Ephraim Goeze in 1773 (kleiner Wasserbär = little water bear). The name Tardigrada means "slow walker" and was given by Lazzaro Spallanzani in 1777. The name water bear comes from the way they walk, reminiscent of a bear's gait. The biggest adults may reach a body length of 1.5 millimetres, the smallest below 0.1 mm. Freshly hatched larvae may be smaller than 0.05 mm.

Tardigrades are polyextremophiles; scientists have reported their existence in hot springs, on top of the Himalayas, under layers of solid ice and in ocean sediments. Many species can be found in a milder environment like lakes, ponds and meadows, while others can be found in stone walls and roofs. Tardigrades are most common in moist environments, but can stay active wherever they can retain at least some moisture.

Tardigrades have been known to withstand the following extremes while in this state:

• * Temperature – tardigrades can survive being heated for a few minutes to 151 °C, or being chilled for days at -200 °C, or for a few minutes at -272 °C (~1 degree above absolute zero).
  
  * Pressure – they can withstand the extremely low pressure of a vacuum and also very high pressures, more than 1,200 times atmospheric pressure. It has recently been demonstrated that tardigrades can survive the vacuum of open space and solar radiation combined for at least 10 days. Recent research has revealed that they can also withstand pressure of 6,000 atmospheres, which is nearly six times the pressure of water in the deepest ocean trench.
  
  * Dehydration – tardigrades have been shown to survive nearly 10 years in a dry state. When encountered by extremely low temperatures, their body composition goes from 85% water to only 3%. As water expands upon freezing, dehydration ensures the tardigrades do not get ripped apart by the freezing ice (as waterless tissues cannot freeze).
  
  * Radiation – tardigrades can withstand median lethal doses of 5,000 Gy (gamma-rays) and 6,200 Gy (heavy ions) in hydrated animals (5 to 10 Gy could be fatal to a human). The only explanation thus far for this ability is that their lowered water state provides fewer reactants for the ionizing radiation.In September 2007, a space launch (Foton-M3) showed that tardigrades can survive the extreme environment of outer space for 10 days. After being rehydrated back on Earth, over 68% of the subjects protected from high-energy UV radiation survived and many of these produced viable embryos, and a handful survived full exposure to solar radiation.
  
  * Environmental toxins – tardigrades can undergo chemobiosis—a cryptobiotic response to high levels of environmental toxins. However, these laboratory results have yet to be verified.

Tardigrades are one of the few groups of species that are capable of reversibly suspending their metabolism and going into a state of cryptobiosis. Several species regularly survive in a dehydrated state for nearly ten years. Depending on the environment they may enter this state via anhydrobiosis, cryobiosis, osmobiosis or anoxybiosis. While in this state their metabolism lowers to less than 0.01% of normal and their water content can drop to 1% of normal. Their ability to remain desiccated for such a long period is largely dependent on the high levels of the non-reducing sugar trehalose, which protects their membranes. In this cryptobiotic state the tardigrade is known as a tun.

More than 1,000 species of tardigrades have been described. The most convenient place to find tardigrades is on lichens and mosses. Other environments are dunes, beaches, soil, and marine or freshwater sediments, where they may occur quite frequently (up to 25,000 animals per litre). Tardigrades often can be found by soaking a piece of moss in spring water. Siberian tardigrades differ from living tardigrades in several ways. They have three pairs of legs rather than four; they have a simplified head morphology; and they have no posterior head appendages. It is considered that they probably represent a stem group of living tardigrades. Tardigrades are eutelic, with all adult tardigrades of the same species having the same number of cells. Some tardigrade species have as many as about 40,000 cells in each adult's body, others have far fewer. Most tardigrades are phytophagous (plant eaters) or bacteriophagous (bacteria eaters), but some are predatory (e.g., Milnesium tardigradum).

The tardigrade body has four segments (not counting the head), four pairs of legs without joints, and feet with four to eight claws each. The cuticle contains chitin and is moulted periodically. The tubular mouth is armed with stylets, which are used to pierce the plant cells, algae, or small invertebrates on which the tardigrades feed, releasing the body fluids or cell contents. The mouth opens into a triradiate, muscular, sucking pharynx. The stylets are lost when the animal moults, and a new pair is secreted from a pair of glands that lie on either side of the mouth. The pharynx connects to a short oesophagus, and then to an intestine that occupies much of the length of the body, which is the main site of digestion. The intestine opens, via a short rectum, to an anus located at the terminal end of the body. Some species only defecate when they moult, leaving the faeces behind with the shed cuticle.

Although some species are parthenogenetic, both males and females are usually present, each with a single gonad located above the intestine. Two ducts run from the testis in males, opening through a single pore in front of the anus. In contrast, females have a single duct opening either just above the anus or directly into the rectum, which thus forms a cloaca.

Tardigrades are oviparous, and fertilisation is usually external. Mating occurs during the moult with the eggs being laid inside the shed cuticle of the female and then covered with sperm. A few species have internal fertilisation, with mating occurring before the female fully sheds her cuticle. In most cases, the eggs are left inside the shed cuticle to develop, but some attach them to the nearby substrate. The eggs hatch after no more than fourteen days, with the young already possessing their full complement of adult cells. Growth to the adult size therefore occurs by enlargement of the individual cells (hypertrophy), rather than by cell division. Tardigrades live for three to thirty months, and may moult up to twelve times.

Recent DNA and RNA sequencing data indicate that tardigrades are the sister group to the arthropods and Onychophora. These groups have been traditionally thought of as close relatives of the annelids, but newer schemes consider them Ecdysozoa, together with the roundworms (Nematoda) and several smaller phyla.Tardigrade genomes vary in size, from about 75 to 800 megabase pairs of DNA. The genome of a tardigrade species, Hypsibius dujardini, is being sequenced at the Broad Institute. Hypsibius dujardini has a compact genome and a generation time of about two weeks, and it can be cultured indefinitely and cryopreserved.>>

Boomer12k wrote:
What happens to neighboring systems when a Supernova goes off?????

http://en.wikipedia.org/wiki/Near-Earth_supernova wrote:
<<A near-Earth supernova is an explosion resulting from the death of a star that occurs close enough to the Earth (roughly less than 100 light-years away) to have noticeable effects on its biosphere. On average, a supernova explosion occurs within 10 parsecs of the Earth every 240 million years. Gamma rays are responsible for most of the adverse effects a supernova can have on a living terrestrial planet. In Earth's case, gamma rays induce a chemical reaction in the upper atmosphere, converting molecular nitrogen into nitrogen oxides, depleting the ozone layer enough to expose the surface to harmful solar and cosmic radiation. Phytoplankton and reef communities would be particularly affected, which could badly deplete the base of the marine food chain. Adrian L. Melott et al. estimated that gamma ray bursts from "dangerously close" supernova explosions occur two or more times per thousand million years, and this has been proposed as the cause of the end Ordovician extinction, which resulted in the death of nearly 60% of the oceanic life on Earth.

Type Ia supernovae are thought to be potentially the most dangerous if they occur close enough to the Earth. Because Type Ia supernovae arise from dim, common white dwarf stars, it is likely that a supernova that could affect the Earth will occur unpredictably and take place in a star system that is not well studied. One theory suggests that a Type Ia supernova would have to be closer than a thousand parsecs (3300 light-years) to affect the Earth. The closest known candidate is IK Pegasi. It is currently estimated, however, that by the time it could become a threat, its velocity in relation to the Solar System would have carried IK Pegasi to a safe distance.

Speculation as to the effects of a nearby supernova on Earth often focuses on large stars as Type II supernova candidates. Several prominent stars within a few hundred light years from the Sun are candidates for becoming supernovae in as little as a millennium. One example is Betelgeuse, a red supergiant 427 light-years from Earth. Though spectacular, these "predictable" supernovae are thought to have little potential to affect Earth.

Recent estimates predict that a Type II supernova would have to be closer than eight parsecs (26 light-years) to destroy half of the Earth's ozone layer. Such estimates are mostly concerned with atmospheric modeling and considered only the known radiation flux from SN 1987A, a Type II supernova in the Large Magellanic Cloud. Estimates of the rate of supernova occurrence within 10 parsecs of the Earth vary from 0.05-0.5 per Ga to 10 per Ga. Several authors have based their estimates on the idea that supernovae are concentrated in the spiral arms of the galaxy, and that supernova explosions near the Sun usually occur during the ~10 million years that the Sun takes to pass through one of these regions (we are now in or entering the Orion arm). The relatively recent paper by Gehrels et al. uses a value of 3 supernovae less than 10 parsecs away per Ga. The frequency within a distance D is proportional to D³ for small values of D, but for larger values is proportional to D² because of the finite thickness of the galactic disk.(at intergalactic distances D³ is again appropriate)Examples of relatively near supernovae are the Vela Supernova Remnant (~800 ly, ~12,000 years ago) and Geminga (~550 ly, ~300,000 years ago).

In 1996, astronomers at the University of Illinois at Urbana-Champaign theorized that traces of past supernovae might be detectable on Earth in the form of metal isotope signatures in rock strata. Subsequently, iron-60 enrichment has been reported in deep-sea rock of the Pacific Ocean by researchers from the Technical University of Munich. This iron isotope (only 23 atoms) was found in the top 2 cm of crust and dates from the last 13 million years or so. It is estimated that the supernova must have occurred in the last 5 million years or else it would have had to have happened very close to the solar system to account for so much iron-60 still being here. A supernova occurring as close as would have been needed would have probably caused a mass extinction, which didn't happen in that timeframe. The quantity of iron seems to indicate that the supernova was less than 30 parsecs away. On the other hand, the authors estimate the frequency of supernovae at a distance less than D (for reasonably small D) as around (D/10 pc)³ per Ga, which gives a probability of only around 5% for a supernova within 30 pc in the last 5 million years. They point out that the probability may be higher because we are entering the Orion arm of the Milky Way.

In 1998 a supernova remnant, RX J0852.0-4622, was found in front (apparently) of the larger Vela Supernova Remnant. Gamma rays from the decay of titanium-44 (half-life 90 years) were independently discovered coming from it, showing that it must have exploded fairly recently (perhaps around 1200 CE), but there is no historical record of it. The flux of gamma rays and x-rays indicates that the supernova was relatively close to us (perhaps 200 parsecs). If so, this is a surprising event because supernovae less than 200 parsecs away are estimated to occur less than once per 100,000 years.

In 2009, researchers have found nitrates in ice cores from Antarctica at depths corresponding to the known supernovae of 1006 and 1054 CE, as well as from around 1060 CE. The nitrates were apparently formed from nitrogen oxides created by gamma rays from the supernovae. This technique should be able to detect supernovae going back several thousand years.>>

garry wrote:
With this being an assumed supernova remnant, why is there such a difference in structure in other so call supernova events say like 1987A? If the mechanism is about the same, then the results should be about the same.